Recently, exhaust purification is an environmentally important problem and in view of air pollution prevention, regulations have become stricter. In order to remove harmful components from exhaust emitted from an internal combustion engine of automobiles or the like or other combustion engines, use of an exhaust purifying catalyst is being carried out.
For example, the exhaust discharged from an engine is purified by a catalyst converter and then released into the air. However, due to low temperature immediately after initiation of engine operation, the catalyst in the catalyst converter is in an inactive state and cannot sufficiently purify the exhaust.
On the other hand, the catalyst used for exhaust purification is generally a catalyst obtained by loading a noble metal such as Ag, Pt and Pd on a support, but such a noble metal is expensive and in view of resources the amount used thereof must be reduced.
On this account, various studies are being made on catalysts.
For example, Kokai (Japanese Unexamined Patent Publication) No. 2007-160168 describes an exhaust purifying apparatus comprising an HC adsorbent material composed of a zeolite ion-exchanged/loaded with at least either one of Pd and Ag, an NOx adsorbent material disposed on the exhaust downstream side of the HC adsorbent material and composed of a zeolite ion-exchanged/loaded with at least one member selected from Fe, Cu and Co, and a CO adsorbent material disposed on the exhaust downstream side of the NOx adsorbent material and obtained by loading Pd on ceria. As specific examples thereof, there is exemplified a case where a model gas consisting of C3H6 as HC, NO2, CO and H2O, with the balance being N2, is flowed at room temperature (25° C.) for 20 seconds and when the adsorption rate is measured, a high adsorption rate is obtained. However, the CO purification rate in the case of flowing the gas continuously in the co-presence of oxygen is unknown.